Losing to Ukip in the Eastleigh by-election would cause a "crisis" in the
Conservative party, a senior Tory has said.

Speaking to BBC Two's Daily Politics, David Davis, a former party leadership candidate, appeared to admit the possibility of the Conservatives coming third behind Ukip and the Liberal Democrats in Thursday's crucial vote.

He said any result showing Ukip polling close behind the Tories would cause worries in the party but dismissed the idea that it would threaten the Prime Minister's leadership.

Mr Davis said: “I think if we came third it would be a crisis, I think that’s the case, and if it’s a close second with UKIP on our tail it will also be uncomfortable.

"Lets be clear, it's not going to dislodge David Cameron. He's going to be there till the next election, but the simple truth is that it will make things more uncomfortable in the House of Commons.”

The Liberal Democrats are thought to be currently in the lead, with the Tories close behind. Ukip is gaining ground on both parties, while Labour is believed to be trailing in fourth position.

The poll is a key test for both Coalition leaders. Mr Cameron will face increasing unrest on his backbenches if the by-election shows the Tories are losing voters to Ukip.

Nick Clegg's leadership of the Lib Dems would also come under pressure if his party fails to hold the seat, amid questions about his handling of the Lord Rennard sexual harrassment allegations.

With less than 24 hours to go before polling stations open, ministers have also been expressing concern that Eastleigh residents might be getting "election fatigue".

The town's residents have been hit with a deluge of pamphlets, doorknockers and telephone canvassing over the last fortnight.

Some households have been pestered up to 15 times a day by the various parties, as the contest enters its final two days. Campaigners are worried that this could hit turnout or increase votes for protest parties.

Patrick McLoughlin, a Tory Cabinet minister, said he thought there is "some truth" in the fear that many are getting fed up with the stream of politicians pestering for their vote.

"I'm afraid it's something that happens in by-elections," he said. "I've spoken to some people today who've been inundated. One lady had been on holiday for two weeks and came back to a mass of literature. It's one of those things where we just have to get the information out."